The Xici zhuan (Appended Statements, one of the Ten Wings) preserves the classical yarrow procedure: take fifty stalks, set one aside, divide the forty-nine in two heaps, and count off by fours through three operations to generate each line, yielding old yang, young yang, young yin, or old yin with unequal probabilities. The dayi, Great Expansion, ritual is the oldest documented hexagram-generation algorithm; coin casting is a later simplification with different odds.
Most modern users throw three coins six times, a method popularized for convenience. Critics note it flattens the probability structure: yarrow produces changing yang lines about three times as often as changing yin lines, while three-coin casting equalizes them, quietly editing the oracle's statistical voice.
The method's poetry is mechanical: you do not ask the stalks, you sort them, and meaning precipitates from what remains. Whether one calls it synchronicity or apophenia, the yarrow ritual is a device for surrendering the choice of answer to a process the querent cannot steer.
If a random sorting of stalks can produce an answer worth obeying, what is the answer actually made of?